Carrier 59MN7B Installation, Start-Up, Operating And Service And Maintenance Instructions page 66

CAUTION
!
FURNACE DAMAGE HAZARD
Failure to follow this caution may result in reduced furnace
life.
DO NOT redrill orifices. Improper drilling (burrs,
out- -of- -round holes, etc.) can cause excessive burner noise
and misdirection of burner flames. This can result in flame
impingement of heat exchangers, causing failures. See Fig.
59.
Fig. 59 - - Orifice Hole
For proper operation and long term reliability, the Furnace input
rate must be within +/- -2 percent of input rate on furnace rating
plate or as adjusted for altitude.
The gas input rate on rating plate is for installations at altitudes up
to 2000 ft. (609.6M).
NOTICE
The NATURAL GAS manifold pressure adjustments in Tables
19 and 20 compensate for BOTH altitude AND gas heating
value. DO NOT apply an additional derate factor to the
pressures show in Table 19 or 20. The values in this table are
NOT referenced to sea level; they are AS- -MEASURED AT
ALTITUDE.
The heating content of natural gas at altitude may already
provide for a reduction in capacity of the furnace. Be sure to
obtain the expected in- -season gas heating value of the gas
from the gas supplier BEFORE making any adjustments for
capacity or altitude. Refer to Table 19 or 20. No adjustments
to the furnace may be necessary at altitude for certain gas
heating values.
Refer to the instructions provided in the factory- -specified
LP/Propane conversion kit for instructions for setting gas
manifold pressures for LP/Propane applications.
In the USA, the input rating for altitudes above 2000 ft. (609.6M)
must be reduced by 2 percent for each 1000 ft. (304.8M) above
sea level. Refer to Table 16.
In Canada, the input rating must be reduced by 5 percent for
altitudes of 2000 ft. (609.6M) to 4500 ft. (1371.6M) above sea
level. The natural gas manifold pressures in Tables 19 and 20
adjust for BOTH altitude and natural gas heating value.
NOTE: For Canadian altitudes of 2000 to 4500 ft. (610 to 1372
M), use USA altitudes of 2001 to 2000 ft. (611 to 914 M) in Table
19.
To adjust manifold pressure to obtain the proper input rate, first,
determine if the furnace has the correct orifice installed. At higher
altitudes or different gas heat contents, it may be necessary to
change the factory orifice to a different orifice. Tables have been
provided in the furnace installation instructions to match the
required orifice to the manifold pressure to the heat content and
specific gravity of the gas.
To do this:
BURNER
ORIFICE
A93059
EXAMPLE: 0 - - 2000 ft. (0 - - 609.6M) altitude
Heating value = 1050 Btu/cu ft.
Specific gravity = 0.62
Therefore: Orifice No. 44
* Furnace is shipped with No. 44 orifices. In this example, all
main burner orifices are the correct size and do not need to be
changed to obtain proper input rate.
Manifold pressure: 3.4- -in. w.c. for maximum heat, 0.55- -in. w.c.
for minimum heat.
NOTE:
multiply the in. w.c. value by 249.1 Pa/in. w.c. (1 in. w.c. = 249.1
Pa).
66
NOTICE
THERE ARE TWO MANIFOLD PRESSURE TABLES
Use Table 19 for all models EXCEPT 59MN7B060C21- -20.
Use Table 20 for Model 59MN7B060C21- -20 ONLY.
1. Obtain average yearly gas heat value (at installed altitude)
from local gas supplier.
2. Obtain average yearly specific gravity from local gas
supplier.
3. Find installation altitude range for your installation in the
manifold pressure tables. See Table 19 for 20,000 Btuh
Max- -Heat/8,000 Btuh min- -heat per burner or Table 20 for
20,200 Btuh Max- -Heat/8,000 Btuh Min- -Heat per burner.
4. Find closest natural gas heat value and specific gravity in
Table 19 or Table 20 depending on furnace gas input rate.
5. Follow heat value and specific gravity lines to point of
intersection to find orifice size and maximum and
minimum manifold pressure settings for proper operation.
6. Check and verify burner orifice size in furnace. NEVER
ASSUME ORIFICE SIZE.
VERIFY.
NOTICE
If orifice hole appears damaged or it is suspected to have been
redrilled, check orifice hole with a numbered drill bit of
correct size. Never redrill an orifice. A burr- -free and squarely
aligned orifice hole is essential for proper flame characteristics.
7. Replace original orifice with correct size, if required by
Table 19 or Table 20 depending on furnace gas input rate.
Use only factory- -supplied orifices. See EXAMPLE 1.
EXAMPLE 1 - - 80,000 BTUH INPUT:
To convert gas manifold Table pressures to Pascals,
ALWAYS CHECK AND